The invention concerns a hydrodynamic mechanical multi-speed compound transmission.
Hydrodynamic mechanical multi-speed compound transmissions, consisting of a hydrodynamic speed/torque converter and a mechanical transmission part, are known in a variety of types. The publication DE 38 04 393 C2 identifies a hydrodynamic multi-speed compound transmission, consisting of a torque converter and a gearbox in series. The gearbox contains two planetary gear trains, where the planet carriers of both planetary gear trains are mutually linked and form the output side of the gearbox. The number of required planetary gear members or planetary gear trains (possibly a Ravigneaux set) may be minimized with such an arrangement, and with an appropriate allocation of gears at least three gear levels can be obtained, which are minimized in length, seen in an axial direction. The hydrodynamic speed/torque converter contains an impeller, a turbine wheel and two stators (a first stator and a second stator) where means are designed to enable the linkage of the turbine wheel and the first stator with the mechanical gears by means of a gearbox. In particular, the overall gearbox input shaft may be linked either with the hydrodynamic speed/torque converter and thus via the turbine wheel with the sun gear of one planetary gear train of the mechanical gear part or directly via a so-called bypass clutch with the same. The first stator is linked via a free-wheel with the sun gear of the second planetary gear train of the mechanical gear part. The characteristics of the hydrodynamic speed/torque converter across the whole range of gear ratios and the gear ratio of the mechanical gearbox are modified by switching the path of transmission of the moment emanating from the first stator shaft, namely by the optional use of linkage and/or brake arrangements, which enable either a lock of the first stator shaft or a linkage of the first stator shaft with the turbine wheel shaft and thus with the first sun gear of the first planetary gear train.
The disadvantage of the transmission described in the publication referenced above consists of the relatively high construction requirement, which increases costs, caused among other reasons by the use of a single level, three phase converter and the availability of support for both of its stators. This transmission yielded good results in the low speed range and the potential low speed range conversion, but some improvements are still required in certain uses.
The publication JP 09079346 A contains an example of a hydrodynamic-mechanical multi-speed compound transmission to provide for five gear levels. This contains a hydrodynamic transmission part in the form of a hydrodynamic speed/torque converter with an impeller, a turbine wheel, a stator located between these two and a gearbox switched in series with them. The gearbox likewise contains two planetary gear trains, where the planet carriers of both planetary gear trains are linked with each other and form the output side of the gearbox. The stator is linked to the planetary gear trains via a freewheel. In order to realize the fourth and fifth gears, a speed/torque converter unit in the form of a planetary gear train is integrated between the turbine wheel and the two planetary gear trains of the mechanical gearbox, which converts the moment of the turbine by a gear to the two planetary gear trains. As used in vehicles, the power transfer via the hydrodynamic speed/torque converter is used only during the low speed range and to a certain extent in the first lower gear. In the remainder of the useable range, the power transfer bypasses the hydrodynamic speed/torque converter, usually by means of a bypass clutch. Of significance for the use of a hydrodynamic speed/torque converter during the low speed range are the following advantages of hydrodynamic power transfer: continuous, with torque conversion, elastic, frictionless and vibration-reducing. Specific requirements are imposed on the transfer process in its linkage with motors for various uses during the low speed range. For use in vehicles, a particular behavior, specifically a particular power transfer by the impeller of the hydrodynamic speed/torque converter is desirable. By means of the linkage between the stator of the hydrodynamic speed/torque converter and the planetary gear trains connected by their shafts, the stator will in certain conditions be impelled in the opposite direction between impeller and turbine wheel. While this solution provides a feasible method to supply several gear speeds in a compact size and simultaneously an improved transfer during the low speed range with a particularly improved conversion during acceleration and improved efficiency, this generally does not suffice to meet all requirements of use. Likewise, the linkage of the additional planetary gear train is cumbersome to design and must be considered during design of the gearbox. Particularly if standard speed/torque converter units are used, the placement or linkage of the additional planetary gear train can be difficult.
Thus, the invention is targeted to a further development of the type of transmission described above, so that it may satisfy the existing use requirements, particularly during the low speed range, while maintaining the advantage of low weight and small size. The transmission is intended specifically for use in the drive train of vehicles or other uses, where an essentially load-free ramping of the drive motor is desired in addition to the advantages of hydrodynamic power transfer. A further objective is the reduction of the construction resource requirements and the costs of the transmission.
The hydrodynamic-mechanical multi-speed compound transmission contains a first hydrodynamic transmission part and an additional second mechanical transmission part. The mechanical transmission part contains at least two planetary gear trains for the realization of at least three gear levels, a first planetary gear train and a second planetary gear train, which are designed and constructed in such a way that in each case one set of matching elements of the first planetary gear train and second planetary gear train can be linked at least indirectly with the transmission input shaft or with an element of the hydrodynamic speed/torque converter and where there is in addition a second set of matching elements, where an element of the first planetary gear train has a fixed linkage with an element of the second planetary gear train, and where this linkage forms the output of the mechanical speed/torque converter, which is linked at least indirectly with the output of the transmission. According to the invention, the hydrodynamic speed/torque converter of the first hydrodynamic transmission part is designed as a single-level two-phase hydrodynamic speed/torque converter. This includes an impeller, a turbine wheel and a stator. According to this embodiment, only a turbine level is included and the reaction member in the form of a stator rotates permanently or only intermittently. According to the invention, this is solved by connecting the stator via a geared member with a solid support or a freewheel with the first planetary gear train. According to the invention, the turbine wheel of the hydrodynamic speed/torque converter has a fixed linkage with the second planetary gear train, i.e. the linkage does no contain intervening or potentially intervening speed/torque converter units. Likewise, this embodiment reduces the power potentially transferred in the power train by an impeller through twist modification of the fluid flow at the flow from the stator to the impeller, particularly for use in vehicles in order to lower energy consumption of the motor in the low speed range for at least a portion of the low speed range. The twist modification is preferentially generated by powering the stator in the direction of rotation opposite to the rotation of the impeller and the turbine wheel. The resulting increase of conversion and improvement of the efficiency is increased by the absence of intervening gears between the turbine wheel and the second planetary gear train, and thus the theoretically higher speed ratio between stator and turbine wheel, compared to the conventional transmission embodiment according to JP 090793476 A.
The solution according to the invention offers the advantage of using a more cost-effective converter and thus the reduction of total costs for the hydrodynamic-mechanical compound transmission. Because the stator of the converter does not transfer the moment to the fixed shaft, but to the first planetary gear train of the mechanical transmission part, the output torque of the hydrodynamic speed/torque converter is increased. At increasing turbine speed of the hydrodynamic converter, the speed of the stator will increase in the opposite direction. This leads to the result of an increase in the low speed conversion and an improvement of the efficiency at low speeds. The moment acting on the impeller, which can be estimated with the aid of fluid dynamics theory according to the impulse moment equation of fluid dynamics, just as for stationary and non-compressable fluids,
Mr=Mxc3x97xcex94(rcr)
will be reduced. The size of the moment depends on the mass flow flowing through the impeller in a given length of time M=xc3x97V, where  designates the density of the fluid in use and V the mass volume, and the difference of the products of the radius r and the circumference component c of the absolute fluid velocity at the inflow and outflow of the impeller in question. Any modification of the inflow and outflow direction on the impeller in question will therefore also modify the moment acting on this impeller. Given the fact that the sum of all moments in a closed system must always equal Zero, these forces will automatically adjust to again satisfy the equilibrium conditions. The following variables are essential core variables of the hydrodynamic energy transfer system, i.e. of a hydrodynamic speed/torque converter:
Input or pump moment Mxcfx81
Output or turbine moment Mxcfx84
Input or pump speed nxcfx81
Output or turbine speed nxcfx84
Efficiency xcex7
The input power of a pump is determined by the product of the input pump moment Mxcfx81 and the acceleration of circulation xcfx89. Given the opposite rotation of the stator to the rotation between impeller and turbine wheel, the fluid flow will be twisted at the point of flow from the stator to the impeller, which is the reason for the modification of the output transfer behavior of the impeller. In addition, conversion at low speeds is increased with this solution, just as for other converter types, but where is critical that the output torque at the turbine wheel remains unchanged compared to conventional solutions, where this effect is obtained through the simultaneous presence of the reduction of the moment acting on the impeller and an increased conversion at low speeds. This makes it possible to reduce the load on the propulsion motor significantly, while maintaining the level of the output torque, even if the corresponding high moment at low speeds is still desired. In terms of the dimensionless efficiency parameter xcex for a hydrodynamic speed/torque converter with a stator, which according to this invention turns in the opposite direction, the load on the propulsion motor varies with the speed of the turbine, and thus, depending on the characteristics, to a different propulsion speed or to a different propulsion moment.
Because the relationship of the torque moment transfer for any given status of the fluid transmission, i.e. for specific values for output and input speed, can be described in a diagram as a quadratic and in the case of power input as a cubic parabola, parabolas with varying slopes result for the torque or power input of the hydrodynamic speed/torque converter for alternative values of input and output speeds.
These curves are then superimposed on the characteristic curve of the motor, so that the intersections of the characteristic curve of the motor, particularly where a combustion engine is used in the motor, with the characteristic curve of the hydrodynamic speed/torque converter will identify the current status of the motor and the converter and their interaction. Whereas an increase in pump speed leads to a reduction of the transferable moment in the case of a conventional hydrodynamic speed/torque converter, the embodiment according to the invention will have a substantially different characteristic curve, where the transferable moment at the impeller is lowered if the ratio of pump speed to turbine speed is below a set value, but where it reverts at higher ratios and conforms to the conventional case.
The preferred embodiment has a linkage of the two planetary gear trains (first planetary gear train and second planetary gear train) of the gear elements in such a way that gear elements of identical types are linked to each other. Here the gear element of the first planetary gear train, which is firmly linked with a gear element of the second planetary gear train, will in each case consists of the planet carrier of the corresponding planetary gear train. The two sun gears of the individual planetary gear trains (first planetary gear train and second planetary gear train) form the inputs to the mechanical speed/torque converter. Here the first input, which is linked to the sun gear of the first planetary gear train, is linked via a freewheel to the stator of the hydrodynamic speed/torque converter. The sun gear of the second planetary gear train is preferentially linked to the turbine wheel shaft, which may be linked via either the hydrodynamic speed/torque converter or via the bypass clutch with the transmission input shaft. The output of the mechanical speed/torque converter can be linked either directly to the output of the transmission or to a further mechanical speed/torque converter in the form of a mechanical overdrive, which is linked in turn with the output or the transmission output shaft.
To realize the various gears, shift arrangements are designed in the form of brake units and clutch units, which are best built with multiple-disk clutches. The various shift arrangements must be used in accordance with the desired gear and the associated gear ratio. This is best designed with a transmission valve.
A first brake arrangement serves to lock the stator shaft and thus the sun gear of the first planetary gear train. A second brake arrangement serves to lock the annulus of the first planetary gear train; a third brake arrangement serves to lock the annulus of the second planetary gear train of the mechanical speed/torque converter. A further fourth brake arrangement serves to lock the sun gear of the overdrive. A first clutch element serves to assure a rotationally solid connection of the sun gear of the first planetary gear train and the sun gear of the second planetary gear train.
Placing the overdrive in the flow of power from the transmission input shaft to the transmission output shaft in a spatial sense behind the mechanical speed/torque converter makes it feasible to generate secondary power outputs. The mere placement of the mechanical overdrive behind the mechanical speed/torque converter forms the first basic configuration, which is characterized by the presence of a multi-speed transmission, specifically a six speed transmission with a simultaneous shortening of the required design space, specifically the design space compared to the basic transmission (3 speed transmission). The overdrive is best designed likewise in the form of a simple planetary gear train, where only one shift element in the form of the fourth brake arrangement is included, which serves to lock the sun gear. Otherwise, the shaft of the mechanical overdrive is linked to the shaft of the mechanical speed/torque converter. Thus it is possible to have three speeds without using a shift element of the overdrive, because the shaft of the overdrive rotates at the same speed as the output of the mechanical speed/torque converter. The output of the overdrive consists of the annulus, which is linked with other speed/torque-transferring elements, such as a spur gear or, depending on the shape of the cogs of the annulus, also a bevel gear. The resulting gear layout must be considered in the layout of the transmission.